Your furniture is definitely modern and fresh but the fireplace is dragging down the rest of the room. If you aren't opposed to painting to resurfacing, some brighter change to the fireplace would be in order. I think that should do the trick and add a few colorful white accent pillows on the dark couch.

I agree-for me, this room would feel cold. But the transition from Traditional to Modern requires a change of vision also. Changing the color of the fireplace is a great idea. I also like bolder colors on the walls. If there is more color available, accenting with white would seem to make the colors 'pop!' Think light-hearted!

I would put some woven shades in the windows on each side of the fireplace. I would add a warm colored textured throw on the sofa. I would add a floor arc lamp next to the recliner. Adding a round coffee table would take the edge of the room;)

Maybe a relaxing water wall to warm things up?

I don't think you need to change the fireplace. It's beautiful and has textural interest. Just fill it with with lots and lots of white birch logs. http://www.wilsonevergreens.com/fireplace-birch-logs.html sells large bundles of them cut to size. An interesting basket or modern container of extra logs in front of the fireplace would add warmth and lightness.

--Search for a much larger painting for over the fireplace. Just do a Google search for brown, blue, abstract painting, and many examples come up. The one below has the blue sky, which echoes the blue sky coming through your windows.

--Find one or two very small, interesting occasional tables to place by your chairs which give a guests a feeling of having a place to set down a drink or coffee cup.

--Add more books to your coffee table and perhaps an interesting tray--again suggesting a place to gather with drinks or read a book.

--A narrow console table on the staircase wall with a lamp, a good-sized interesting mirror, and a pottery bowl in blue would look welcoming as you come in the door. The mirror would reflect the living room.

--Another possibility, if the furniture measurements work, is to rearrange the furniture. Float the coach, with a beautiful blue throw off the back, so that it faces the fireplace. Place the leather chair by the fireplace with the leather stool in front of it--this suggests a "reading by the fireplace" vibe. Keep the print chair near the other window as it is now.

You just have to get used to the room, but it's certainly not cold. Biggest impact will be your focal point - the fireplace. Replace what is above and for sure your room will instantly change. Add art to other two walls. If you can get the fabric in your drapes, use for roman blinds on the two windows (or bamboo type shades), change items on coffee table for more interest. Move plant from next to couch (seems squeezed in) to opposite wall and couche pillows should be a bit more coordinated (add one to the leather chair). Try pushing back the graphic chair into corner and try ottoman in front of fireplace, as it's seems awkward.

A big silver or white sunburst mirror above the fireplace and a really soft and furry blanket folded and draped over one side of the sofa.

A large painting or two with some color would brighten up your room. A vertical picture near the brown chair and a horizontal for over the fireplace.

These are from etsy.com

To decide what colours will give the room pop, collect scarves, table cloths, bedcovers - anything with warm colours - and try them against what you already have, before you make any changes.
I am opposed to painting brickwork because you can't get it back....
I think you could warm up the room with a large square-ish painting in warm colours - could be pop art, abstract, whatever, but modern, not ye olde, since you want a modern look. Actually your present colour scheme is rather dull, and you seem to have used the colder colours in the brickwork for your accent chair and cushions. To brighten it, try a rust coloured throw on the sofa, this will warm up the room.
I think I'd put roman blinds in bamboo or a warm tan on the windows flanking the fireplace. You have what looks like a leather chair there in a nice tan, use that colour.
And I think a round coffee table in such a confined space would be better. I like the square table you have, but if you look at the pattern you have on the chair, they are arcs and circles - a round table would look so much more interesting and has no corners to catch your legs! Maybe that square table could go elsewhere?
I also think that next time you could paint the room a warm buff or a paler version of the brickwork colours would be nicer than the present grey, which can look dark, not to say cold, and works best teamed with warm bright colours. Unless the room is very sunny grey rarely looks good, especially under artificial light.

Try Wyndham creme on the walls - it reads as a lovely warm yellow (Benjamin Moore)

I like the fireplace as is. At first I was going to suggest painting the walls, but I really think you just need some artwork. You are going in a nice direction, it just doesn't feel finished yet. Go with something larger over the mantle and find another place in the room for the art that is currently there. You also need to add some floor lamps. I'm not a fan of the sconces but after you add other lighting and some artwork maybe they won't be as noticeable.

The picture over the FP echoes the angular lines of the entire FP wall and windows..
A dose of antiqued gold accessories and curves will lift and brighten up your modern space:

Then edit your pillow collection. Take for instance the aqua pillow. Replace with an aqua with gold in it to echo the accents. Some additions to consider:

I would go for a timber coffee table to draw some attention away from fire and toward the seating area. Then add some colour in cushions and some books or candles on coffee table. Black metal table seems Spanish and at odds with rest of room.

This room just needs people in it to warm it up. The colors, fireplace, and furniture look great.

The big wall needs something, could be anything but personally I would decorate it with objects that reflect the people living here - photos, personal collection(s), even crayon scribble art if you have any curtain climbers around to make you some. I'd avoid hanging any kind of print or preframed piece from a big box, which might inject the "cold" you're trying to steer away from.

Thanks everyone so much for all your input! You've all given me a lot of food for thought! Here's a before pic of the living room so you can see how far we've come.

I think I would have kept the mantle-shelf darker, it seems to jump out at you rather. Adding blinds to the small windows in a warm colour, and putting a picture in similar warm colours would go a long way to brighten the room. You could experiment with a variety of coloured throws for the seasons.

I would replace the mini-print pale curtains with a more vibrant print. Definitely remove the sheers.

What a beautiful transformation - so much more modern.

I love the room now! What a transformation. I agree with the people who have said all you really need is some lovely artwork. You have done a truly amazing job re-visioning this room. Well done.

I would say a large mirror over the fireplace would catch the sun coming though the windows behind and let on a fabulous bright natural light.

Add a touch of yellow. Maybe a couple framed prints that have yellow in it and a yellow throw.

Adding fabric roman shades or valances (using the same fabric as the curtains) will help warm up the fireplace wall.

Everything in your room is very linear. Adding some round elements - round mirror above the fireplace, changing your coffee table to a round one - will add some softness (and warmth) to the space without compromising your modern look. Nice job, by the way. I love your sofa. Where did you purchase it?

Hoping the poster comes back with some updates as it has been awhile.

Oops - just noticed the dates. Yes, it's been a while. I got caught up in another opportunity to photoshop. I've gotta get a life!

Change painting, put larger painting in. Something with interest and great colors. Accents pillows with colors from painting.
Possibly a large tall and thin palm in the right side